[Linux] delete all data except 4 file newest

#______________________DELETE_OLD_DATA:BEGIN
#Source: https://stackoverflow.com/questions/25785/delete-all-but-the-most-recent-x-files-in-bash

FOLDER_DST=/opt/bk
mkdir -p $FOLDER_DST
cd $FOLDER_DST

#Giu lai 4 file moi nhat trong thu muc [$FOLDER_DST]:
rm  -rf `ls -t | awk 'NR>4'`

#______________________DELETE_OLD_DATA:END





#/opt/script/fwsync-HOST01_2_HOST02.sh
#LastUpdate: #09:38 2018.12.23
#################################################
#FILE_NAME=fwsync-HOST01_2_HOST02.sh
#HA_VHOST=/opt/script
#cat $HA_VHOST/$FILE_NAME | grep LastUpdate
#################################################
#SYNC FW:
#0 */1 * * * /opt/script/fwsync-HOST01_2_HOST02.sh
#################################################

#__________________________________CONTENT:BEGIN
HOST01=srv186_HaProxy01
HOST02=srv187_HaProxy02

#1/ BACKUP $HOST02 CONFIG:
ssh -p 65022 root@$HOST02 "\
mkdir -p /etc/iptables;\
cd /etc/iptables;\
rm -rf *.bk;\
cp -vR /etc/iptables/rules.v4 /etc/iptables/rules.v4-[$HOSTNAME]-[$(date +'%Y.%m.%d-%H.%M.%S.%3N')].bk;
"
#


#2/ SYNC 100% CONFIG FROM HOST01->HOST02:
rsync -avz -e "ssh -p 65022" /etc/iptables/rules.v4 root@$HOST02:/etc/iptables/rules.v4

#__________________________________CONTENT:END

#THE-END

##rm -rf `ls -t *.bk | awk 'NR>4'`;\